Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write.
In a modern magnetic hard disk drive device, each head is a sub-component of a head-gimbal assembly (HGA) that typically includes a laminated flexure to carry the electrical signals to and from the head. The HGA, in turn, is a sub-component of a head-stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flexible printed circuit (FPC). The plurality of HGAs are attached to various arms of the actuator.
Modern laminated flexures typically include conductive copper traces that are isolated from a stainless steel structural layer by a polyimide dielectric layer. So that the signals from/to the head can reach the FPC on the actuator body, each HGA flexure includes a flexure tail that extends away from the head along a corresponding actuator arm and ultimately attaches to the FPC adjacent the actuator body. That is, the flexure includes traces that extend from adjacent the head and continue along the flexure tail to electrical connection points. The FPC includes conductive electrical terminals that correspond to the electrical connection points of the flexure tail.
To facilitate electrical connection of the conductive traces of the flexure tails to the conductive electrical terminals of the FPC during the HSA manufacturing process, the flexure tails must first be properly positioned relative to the FPC so that the conductive traces of the flexure tails are aligned with the conductive electrical terminals of the FPC. Then the flexure tails must be held or constrained against the conductive electrical terminals of the FPC while the aforementioned electrical connections are made. Such electrical connections may be made by ultrasonic bonding, which is a process during which ultrasonic wave energy is applied by a tool tip that presses upon bond pads of the flexure tail, to cause a gold plating on the flexure tail bond pads to join another gold plating upon the electrical terminals of the FPC.
However, recently for some disk drive products, flexure tail to FPC electrical connections may employ a type of anisotropic conductive film (ACF) bonding. An anisotropic conductive film is typically an adhesive doped with conductive beads or cylindrical particles of uniform or similar diameter. As the doped adhesive is compressed and cured, it is squeezed between the surfaces to be bonded with sufficient uniform pressure that a single layer of the conductive beads makes contact with both surfaces to be bonded. In this way, the thickness of the adhesive layer between the bonded surfaces becomes approximately equal to the size of the conductive beads. The cured adhesive film may conduct electricity via the contacting beads in a direction normal to the bonded surfaces (though may not necessarily conduct electricity parallel to the bonded surfaces, since the beads may not touch each other laterally—though axially each bead is forced to contact both of the surfaces to be bonded—hence the term “anisotropic”).
The flexure tail design requirements to enable or facilitate ACF bonding contrast with those for ultrasonic bonding. For example, ultrasonic bonding pads need only accommodate contact by a relatively small tool tip, while designs for ACF bonding are designed to accommodate a larger bonding tool called a “thermode,” which applies a more uniform pressure and heat to the bond pad(s) during adhesive curing. The uniform pressure and heat may cause a single layer of conductive beads in an ACF to make contact with both opposing surfaces to be bonded. Also, for example, the conductivity through the beads of a cured ACF bond is substantially less than that of the intimate gold contact of an ultrasonic bond, and so the cured ACF bond must cover a larger area in order to present acceptable net conductance.
However, industrial decisions affecting manufacturing facilities and equipment, operator training, parts and materials flow through the factory, inventory, etc, might be given more freedom if the same flexure tail design could facilitate both ACF bonding or ultrasonic bonding. For example, there is a need in the art for a manufacturing manager to be free to direct the same manufacturing lot of HGAs to be bonded by either ultrasonic bonding or by ACF bonding. Accordingly, there is a need in the art for an improved HGA design that can facilitate bonding by either ultrasonic bonding or ACF bonding, during HSA manufacture.